Previous PZT drive circuits for use in cleaning machines are believed to have selected center design frequencies such as 40 kHz and then modulated the center drive frequency at frequencies as high as +/−1.0 khz. The resulting output drive voltage to the PZT load was then also modulated as a result of rectification of the input line voltage that provided a ripple at 120 Hz. The resulting amplitude modulation was high approaching 100% and thereby requiring a higher peak resonant PZT drive voltage to obtain the same average power into the PZT transducer. The result was a lower overall efficiency and increased stress on all components of the system without an improvement in the cleaning result.